The present invention relates to a method for forming a multi-color image by selectively and thermally transferring two chromatic color heat sensitive ink layers onto an image receptor by means of a thermal transfer printer such as a printer, with a thermal head.
Conventionally, full-color expression by thermal transfer was performed by utilizing colors obtained by a subtractive color mixing wherein three colors, cyan (C), magenta (M) and yellow (Y), which are process colors, or four colors, further including black (BK), were superimposed.
Although a high-quality color image with colors close to natural colors can be obtained, this method has a disadvantage in that the image data for outputting the image tends to become immense. Further, upon outputting the image, it is necessary to superimpose the colors three or four times, and hence, the method consumes time and ink ribbons.
Depending on the type of image, some do not need to have a high-quality and wide color reproductivity, like the above-described image. For example, in the case for instruction manuals for appliances, diagrammatic figures of appliances, and the like, it is preferable to obtain an image at low cost and high speed rather than with color reproductivity.
To address the above-described requirements, the present inventors tried to form a multi-color image by thermal transfer using only two color ink ribbons. However, the color expression ranges were narrow. Also, a natural color expression could not be obtained even if two conventionally used process colors selected from cyan (C), magenta (M), yellow (Y), and black (BK) were used in combination, and the combinations of these two colors were found practically useless although high speed could be achieved. Further, it was especially difficult to obtain excellent shadow parts (black parts) by the foregoing two color combinations, resulting in a failure to obtain a sharp and high-quality image.
In view of the foregoing, it is an object of the present invention to provide a thermal transfer image formation method capable of easily performing pseudo-full-color expression using two color ink ribbons while minimizing cost and time.
This and other objects of the present invention will become apparent from the description hereinafter.
The present invention provides a method for forming an image by thermal transfer:
comprising forming a multi-color image using two chromatic color thermal transfer ink ribbons A and B,
the thermal transfer ink ribbons A and B having respective chromatic colors which satisfy the following relations:
YA+YBxe2x89xa71.0
MA+MBxe2x89xa71.0
CA+CBxe2x89xa71.0
wherein YA, MA, and CA are defined respectively as values obtained by color separation of the optical reflection density of the thermal transfer ink ribbon A into Y, M, and C components, and YB, MB, and CB are defined respectively as values obtained by color separation of the optical reflection density of the thermal transfer ink ribbon B into Y, M, and C components.